You must be able to hear the back-up warning signal of a vehicle from at least 10 metres away.
200 feet
200 ft
http://wiki.answers.com/Q/A_horn_must_be_loud_enough_to_hear_within_how_many_feet"
200 feet
Must be able to track the vehicle's location
No one being able to hear them scream.
1000 feet
All instruments you can see and hear, provided you have the ability. In order for it to be an instrument, it must be able to produce sound.
4'8''.
A whistle or horn
This means the horn must be fully outlined.